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The recent rise in whooping cough cases could be caused by a new mutation of the bacteria, according to new findings by a local researcher.

Dr. Alan Evangelista, Director of Microbiology at St. Christopher’s Hospital for Children, is one of three U.S. researchers who discovered mutations of the pertussis bacteria. Their findings were published today in the New England Journal of Medicine.

“The organism has adapted to evade one part of the immune response,” Dr. Evangelista said. “It may be a contributing factor for the rise in the number of cases.”

Whooping cough gets its name for the whooping sound an infected person makes when they cough. The upper respiratory infection is highly contagious and can be spread quickly through coughing or sneezing.

Dr. Evangelista says whooping cough cases jumped nationwide last year to levels not seen in more than half a century. The Centers for Disease Control and Prevention recorded 41,880 cases of pertussis in 2012, the most since 1955.

During 2012, Pennsylvania reported 1,842 cases, 748 cases in New Jersey and 54 in Delaware, according to the CDC. That's a two-to-three-fold increase from 2011.

To uncover the new strain, researchers collected samples from 12 St. Christopher's patients with whooping cough. In 11 cases, they found the pertussis bacteria was no longer producing one of three elements -- a protein called pertactin -- which the immune system uses to identify and fight the disease.

“So your lineman and your linebacker can see the bacteria, but the safeties and cornerbacks don’t see it,” Dr. Evangelista says.

Dr. Evangelista says the goal of the research is to increase awareness and possibly improve the vaccine.

The current pertussis vaccine was introduced in 1995 and updated in 2007, according to Dr. Evangelista. The vaccine is given through a series of shots at 2, 4, 6 and 15-months of age and around age 5, according to the CDC. Booster shots are given as a child ages around age 10. Those over 65-years-old were recommended to get the vaccine about two years ago.

Dr. Evangelista says the vaccine still works, but may not be as effective. He stresses that it is important to continue vaccinating and that further studies are needed.

St. Christopher's Hospital for Children, located in the Hunting Park section of Philadelphia, is one of only a few hospitals nationwide that save and freeze pertussis cultures. They plan to conduct further studies on the mutation. The 137-year-old hospital sees more than 70,000 emergency room patients a year.